Summary: Two decades after its discovery PCR have completely changed clinical practice. PCR is a gold standard method for detecting and identifying pathogen. By observing viral load it allows to predict disease progression and therefore design a better treatment. It is allowing non invasive prenatal diagnosis of many genetic defects. There are few limitations however at the rate PCR is advancing, no doubt in future whole clinical practice will be dependent on PCR.
Background: Polymerase Chain reaction (PCR) is an in vitro process that enables exponential amplification of the define target DNA sequence. The process involves three steps: denaturation, annealing and elongation. In the first step, the reaction mixture containing target DNA, pair of primers, dNTPs, Mg2+, buffer solution and TaqI DNA polymerase is heated around 950 C. This disrupts the hydrogen bonds of double helix. In the second stage lowering the temperature to around 560 C allows the annealing of primer to the single stranded DNA. TaqI DNA polymerase works best at 70-750 C. So the reaction mixture is heated around 750 in the elongation process. In this step TaqI DNA polymerase synthesizes new complementary DNA strand to the single strand of DNA. The process is repeated leading to exponential production of 2n sequence copies (where n is the number of cylce).(1)
PCR was developed by Dr. Kerry Mullis in 1983 while working at the Cetus Corporation. The basis of the idea came from the pioneering work of Gobind Khorana in 1971, who initially described the basic principles DNA replication by using primers. In addition, Cetus Corporation discovered the method of controlling DNA polymerase activity at specific points of a single strand of DNA at the time of Dr. Mullis’s work. This lead to the discovery of PCR by Dr. Kerry Mullis and he was awarded Nobel Prize in chemistry ten years later.(2)
Introduction: Since its discovery, Polymerase Chain reaction (PCR) has been used in vast range of application. This includes prenatal diagnosis of gene mutations, diagnostic detection of target DNA sequence, genome scanning for mutation and forensic matching of scanty cellular DNA with individual suspect. But one of its greatest contributions has been in clinical practice. The purpose of the essay is to discuss how PCR have revolutionised clinical practice.
Method: PubMed Central (The U.S. National Institution of Health) has been used predominantly as a source of primary literature. Some secondary literature has been used for definitions and to advance the understanding the methods of PCR. Search engine also have been used throughout the essay for other journal and websites.
Discussion: Prenatal diagnosis of sickle cell anaemia is one of the applications of PCR with high sensitivity and specificity. Before the advancement of PCR, it used to take several weeks to perform hybridization with a probe by using southern blot but now this is done within 24 hours.(3) PCR also can be employed...